Source, Etc

Dalmatian insect flowers are the unexpanded flower-heads of Chrysanthemum cinerarioefolium, Visiani (N.O. Compositae), a native of Dalmatia, Herzegovina, and Montenegro, and cultivated there as well as in Japan and California.

The flowers of several composite plants have long been known to possess the remarkable property of stupefying flies and other small insects. None, however, appears to act so energetically as insect flowers, and these are most active if collected when they are fully developed, but before they expand. They are then known commercially as ' closed ' flowers, ' half-closed ' and ' open ' flowers being collected at more advanced stages of development. They retain their insecticidal properties indefinitely, even in the state of dry powder. The leaves have been shown to be destitute of insecticidal properties.

Description

The closed flowerheads of commerce are of a dull brownish yellow or greyish brown colour and about 10 mm. in diameter. The bracts of the involucre, which are arranged in two or three rows, are yellowish or greyish in colour, lanceolate, hairy, and membranous at the margin. In the closed flowers they are erect, but as the flowers expand they bend outwards, the capitulum assuming a flattened hemispherical shape. There is only one row of ray-florets, with brownish or whitish ligulate corollas. The disc-florets, which are numerous, have comparatively short yellow corollas. The fruit is longer than the corolla, club-shaped, and provided with five ribs that project so strongly as to make it appear almost winged. Both the corolla and the fruit are sprinkled with yellow shining oil-glands. After the corolla has been removed, the calyx may be seen in the form of a raised membranous ring crowning the fruit. The receptacle is naked and nearly flat.

' Closed' flowers are sub-globular or sub-conical in shape, and usually bear the yellowish, shrivelled, ligulate corollas; ' half-closed ' flowers are nearly hemispherical in shape, and the corollas of the ray-florets are more spreading; ' open ' flowers are still flatter, and most of the ligulate corollas have been broken off; they are often devoid of the tubular corollas of the disc-florets also, and then present a reticulated appearance due to the membranous calices crowning the closely packed fruits.

Insect flowers possess a bitter, acrid taste; the odour is aromatic, but not strong.

The student should observe

(a) The sub-globular or sub-conical shape of the ' closed ' flowers,

(b) The yellowish colour of the bracts,

(c) The short corolla and membranous calyx of the tubular florets,

(d) The five prominent ribs of the fruit.

Constituents

Dalmatian insect flowers contain up to 1.25 per cent, of volatile oil, but the toxic principle is a yellow syrupy substance, pyrethrone, which is an ester yielding by saponification pyrethrol. Pyretol and pyrethrotoxic acid, also given as the active constituent, appear to consist essentially of pyrethrone. It is not volatile, and the flowers do not lose their activity when exposed to the air.

Substances of alkaloidal and glucosidal nature have also been isolated, but our knowledge of them is very imperfect.

Good insect powder should stupefy common house-flies kept near it within a minute; less active powders may take as much as twenty minutes to effect this. It should yield about 8 or 9 per cent, of ash and about 10 per cent, of moisture. The quality of the powder is also indicated by the ethereal extract, good closed flowers affording from 7.5 to 10.5 per cent, of yellow extract; half-closed flowers yield from 6 to 7 per cent., and open flowers from 5 to 6 per cent., while the presence of much stem or leaf is indicated by the greenish colour of the extract.

Substitutes, Etc

Chrysanthemumc occineum, Willdenow, (C. roseum, Weber et Mohr), a native of the Caucasus and northern Persia, yields the Persian (or Caucasian) insect flowers, which were formerly more commonly used than the Dalmatian. The importation has now, however, practically ceased.

The flowerheads are distinguished from the Dalmatian by the dark, nearly black, colour of the involucral bracts, by the rose colour of the ray-florets, and by the ten-ribbed fruit. They are said to be less active than the Dalmatian.

Insect powder may be adulterated with powdered leaves and stems, with the powder of other composite flowers, with lead chromate, etc.; powdered quassia, pepper, aloes, euphorbium, etc., are said to have been found in it.

Use

Powdered insect flowers and also a tincture prepared from them are used to stupefy smalt insects.